LYSOSOMES AS CELLULAR MARKERS OF ENVIRONMENTAL-POLLUTION - TIME-DEPENDENT AND DOSE-DEPENDENT RESPONSES OF THE DIGESTIVE LYSOSOMAL SYSTEM OFMUSSELS AFTER PETROLEUM HYDROCARBON EXPOSURE

Lysosomes are cell organelles containing hydrolytic enzymes and involv ed in intracellular digestion. Numerous environmental contaminants can interfere with lysosomes, and the purpose of the present work was to quantify changes induced by petroleum hydrocarbons on the structure of the lysosomal system of mussel digestive cells. Mussels, Mytilus gall oprovincialis Lmk., were exposed for three months to the water accommo dated fraction (WAF) of two crude oils (URAL and MAYA) and of a lubric ant oil. Three different exposure doses (0.6, 6, and 40% WAF) were use d for each type of hydrocarbon and mussels were sampled at different t ime intervals (days 21, 49, and 91). A stereological study, using an a utomated image analysis system, was made on sections stained for demon stration of beta-glucuronidase activity and four parameters were calcu lated: lysosomal volume density, surface density, surface to volume ra tio, and numerical density. The results indicate that the effect of th e exposure dose on lysosomal structure is variable and there is no lin ear relationship of lysosomal changes with dose. Regarding the effect of the exposure time, two different responses were evidenced: (a) a sh ort-term response (at day 21) with a decrease in size and numbers of l ysosomes and (b) a long-term response (at days 49 and 91) with an incr ease in lysosomal size and a decrease in their numbers. The short-term response may be due to a disintegration process of the digestive cell s with subsequent loss of lysosomes and could represent an adaptative response to hydrocarbon exposure. At long exposure times, lysosomal ch anges, apparently caused by fusion processes giving rise to enlarged l ysosomes, correspond to a ''general stress response.'' (C) 1995 by Joh n Wiley & Sons, Inc.